The compound pentafluoroethane (CF3CHF2 or HFC-125) is useful as a blowing agent, propellant, refregerant, fire extinguishing agent, or sterilant carrier gas. It is desirable for its zero ozone depletion potential.
Various methods for the preparation of pentafluoroethane have been disclosed. U.S. Pat. No. 3,755,477 describes a process for producing fluorinated hydrocarbons using a chromia catalyst prepared by treating a chromium hydroxide paste with water or steam before it is dried and calcined. Example 23 illustrates the conversion of tetrachloroethylene to a product mixture containing CF3CHCl2 (20%), CF3CHClF (20%), CF3CHF2 (30%), and CF3CClF2 (20%); and Example 25 illustrates the conversion of CF3CHCl2 to a product mixture containing CF3CHClF (21%), CF3CHF2 (67%) and CF3CClF2 (2.5%). Chloropentafluoroethane (CF3CClF2 or CFC-115) is objectionable because it represents a yield loss and it is difficult to separate from pentafluoroethane by distillation.
U. S. Pat. No. 3,258,500 describes a process for the catalytic vapor-phase fluorination of certain halohydrocarbons employing a catalyst that consists essentially of an activated anhydrous chromium (III) oxide. Example 17 illustrates the conversion of tetrachloroethylene to a product mixture containing inter alia CF3CHCl2 (3.5%), CF3CHClF (9.2%), and CF3CHF2 (35.0%) at 400° C. and to a product mixture containing inter alia CF3CHCl2 (16.0%), CF3CHClF (38.3%), and CF3CHF2 (25.4%) at 300° C.; and Example 20 illustrates the conversion of chlorotrifluoroethylene to a product mixture containing inter alia CF3CHF2 (26.8%) at 400° C.
Canadian Patent 849,024 and Canadian Patent 1,196,345 also disclose processes employing chromium-containing catalysts that may be used to produce pentafluroethane.
U. S. Pat. No. 4,843,181 discloses a gas phase process for the manufacture of CF3CHCl2 and/or CF3CHClF by contacting a suitable tetrahaloethylene and/or pentahaloethane with HF in the presence of Cr2O3 prepared by the pyrolysis of (NH4)2Cr2O7, the reaction being conducted under controlled conditions whereby the production of CF3CClF2 is minimized.
There is a need for other useful methods of preparing CF3CHF2 where the amount of chloropentafluoroethane by-product is low.